7. F9 Again, from Table 35, page 202 of Timoshenko: M -0.0513 (a) 2 P X 0 M = -20.52 P X 0 Here, the difference between the one term Rayleigh-Ritz Solution and Timoshenko's Solution is approximately 17%. For the purposes of the present analysis the results of the one term Rayleigh-Ritz approximation are considered sufficiently accurate. It is now necessary to propose a stiffener design and incorporate its EI into the moment equation derived from the Rayleigh-Ritz Solution. Although it is acknowledged that many more efficient sections are available, ease of both analysis and manufacture prompt the choice of a rectangular cross section stiffener for this preliminary design. The stiffener is arbitrarily assumed to be four times as deep as it is thick, and the thickness is assumed to be equal to the thickness of the inner hull plate. Thus, the section moment of inertia may be calculated with respect to both an axis through the stiffener center of gravity and the plate neutral axis: t(4t) 3 t4 I s t iff = _ 1_2_ = 5 · 333 INA Istiff + t(4t) d2 Assume: d h t 3 t 2 - 2 2 d2 ¾ t 2 INA 5.333 t4 + 4t 2 (2.25 t2) INA 14.333 t4
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